Easily transportable devices with wireless telecommunications capabilities, such as mobile telephones, personal digital assistants, handheld computers, and similar devices, will be referred to herein as mobile devices or mobile stations. A communications connection between two mobile devices can be referred to as a call or a session. Some mobile devices communicate in a circuit switched mode, wherein a dedicated communication path exists between two devices. For the duration of a call or session, all data exchanged between the two devices travels along the single path.
Some mobile devices also have the capability to communicate in a packet switched mode. In packet switching, a data stream representing a portion of a call or session is divided into packets that are given unique identifiers. The packets might then be transmitted from a source to a destination along different paths and might arrive at the destination at different times. Upon reaching the destination, the packets are reassembled into their original sequence based on the identifiers. In particular, the IP Multimedia Subsystem (IMS) is a packet switched technology that allows multimedia content to be wirelessly transmitted between mobile devices. The term IMS will be used herein to refer to any packet switched network or technology.